<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>css层叠性</title>
    <style type="text/css">
    .box{
        width: 200px;
        height: 80px;
        background: #ccc;
        border: 8px  solid #f00;
        padding: 15px;
        margin-top: 100px;
        margin-left: 100px;
        margin: 20px;
        padding: 100px;
        padding-top: 100px;
        border-radius: 50%
    }

    </style>   
</head>
<body>
<P class="box">这是一个盒子</P> 
</body>
</html>